The present invention relates generally to operations performed in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides a valve used to control actuation of a tool positioned within the well and associated methods.
It is well known in the art to actuate a tool positioned within a subterranean well in response to hydrostatic pressure in the well. For example, U.S. Pat. No. 5,492,173 discloses a tool which includes an activation mechanism responsive to such hydrostatic pressure. The disclosure of that patent is incorporated herein by this reference.
The activation mechanism causes power to be supplied to a control circuit when the hydrostatic pressure reaches a predetermined amount. Thereafter, as the tool is lowered in the well, a timer determines when the power will be supplied to a motor in order to set a lock or plug within the well at an appropriate location. An accelerometer may also be utilized to reset the timer as the tool is displaced in the well, so that the lock or plug is not inadvertently set before the tool has arrived at the appropriate location.
Where the accelerometer is not utilized, the timer is set before the tool enters the well. This timer setting is based on an estimate of the time required to lower the tool to the appropriate location within the well. Unfortunately, this estimate may be incorrect, perhaps due to unforeseen difficulties in lowering the tool in the well, in which case it is likely that the lock or plug will be set prior to reaching the appropriate location. For example, an obstruction may be present in the wellbore or a portion of the wellbore may be deviated from vertical sufficiently far to impede lowering of the tool therein.
Of course, it is well known to displace a tool through a deviated portion of a well by attaching the tool to tubing, such as coiled tubing, and essentially push the tool through the wellbore. However, the use of tubing for this, or another, purpose presents other problems in actuating the tool. For example, it is generally considered uneconomical to perform a trial run with the tubing in order to gain an accurate estimate of the time required to lower the tool to the appropriate location for setting the lock or plug. Therefore, the timer setting estimate may be based on conjecture alone. As another example, if it is desired to utilize the accelerometer to periodically reset the timer as the tool is being lowered in the well, the tubing will typically not accelerate or decelerate at a sufficient level required to excite the accelerometer, due to the mass of the tubing.
Additionally, calculations of hydrostatic pressure in a well are frequently inaccurate. Such inaccuracies may occur due to human error, inaccurate measurement of fluid weight, inaccurate measurement of well deviation, inaccurate measurement of true vertical depth, etc. Since it is the hydrostatic pressure which has been utilized in the past to begin operation of the timer, such inaccuracies also affect the location at which the lock or plug is set by the tool.
The above circumstances may also apply to other tools which rely on fluid pressure within a well for their actuation. For example, in some cases firing heads utilized with perforating guns, setting tools, tubing cutters, etc. utilize fluid pressure for their actuation. Other tools, which do not presently rely on fluid pressure for their actuation for one or more of the above reasons, could be actuated by fluid pressure if the above problems could be resolved satisfactorily.
From the foregoing, it can be seen that it would be quite desirable to provide a means of actuating a tool or accomplishing another objective which does not require a predetermined hydrostatic pressure for its operation, but which actuates the tool or accomplishes its objective in response to an event which may be predictably controlled from the earth's surface. It is accordingly an object of the present invention to provide such an apparatus and associated methods of using the apparatus.